45G 



METAMORPHOSIS OF CRUSTACEA. 



gland, are in opposition to such an opinion. Indeed, we 

 cannot but perceive in this curious animal a repetition of the 

 singular metamorphosis of the Cirripedes, and of some others 

 which I hope shortly to make known, in all of which the 

 animal in its last stage, contrary to what we observe in insects, 

 is less perfect and more simple in structure than its larva ! 



In the first stage of the Sacculina, it is free, provided with 

 a remarkably powerful natatory apparatus, with sight, lives to 

 acquire a comparatively large size, and having fastened upon 

 the crab destined for its future support, insinuates itself, first 

 under the tail flap, and then penetrates the rectum of its 

 victim, and there undergoes its very singular metamorphosis; 

 and from being little larger than a pin's head, acquires such a 

 remarkable bulk as to exceed in width the flap or tail part 

 even of the female crab, and to weigh as much as a quarter of 

 an ounce, and probably contain a million of ova ! This there- 

 fore, comparatively to the size of the animal from which it 

 derives its support, is the largest parasite known, and must 

 incommode the crab in proportion to its growth and number, 

 independent of opening a way for the attachment of barnacles, 

 Serpuli and Zoophiles. From its prodigious fertility, and not 

 even one-tenth of the crabs being so infested, numbers must be 

 devoured in its first or free stage ; it is in this way that it 

 probably contributes to the grand scheme of creation, as in its 

 second stage it appears to live merely to prolong its own race, 

 and may have its use in filling up some link in the scale of 

 natural affinities. 



Thus I have no doubt but it will eventually tend to diminish 

 the apparent interval between the Balani and Lepades, should 

 the advanced larva of the latter be found to become binocular, 

 which is more than probable, considering their perfect resem- 

 blance in their nascent state. 



REFERENCES TO THE FIGURES. 



Fig. 1 . Parasite of Carcinus Manas, as 

 attached to the rectum of the crab, 

 and showing its lower opening. 

 Natural size. 



Fig. 2. The other side of the same. 



Fig. 4. The larva of Sacculina Carcini, 

 when first hatched. Magnified. 



Fig. 5. The supposed larva when fully 

 grown, magnified ; a horns, at the 

 base of which its three eyes are 

 seen, s the five spines of the 

 dorsal clypeus. 



Fig. 6. A copy of Slabber's figure, the 

 Argulus Armiger of Latreille. 



Fig. 3. The testicular gland ; a broad 

 upper attachment, d lower narrow 

 attachment, c puckered edge, by 

 which one side is attached to the 

 enveloping tegument, e its oppo- 

 site free edge, b the translucent 

 organ, supposed to be the stomach 

 (?) of the animal, firmly lodged in 

 a cavity on one shoulder of the 

 gland. 



